New to Java

I'm sorry this is so basic, but I honestly do not know how to do this nor can I find anything online here or anywhere via Google to help me with this one.

I have a JAR file that I created on another machine using JDK 1.6.0 and NetBeans 5.5 on WinXP.

I copied and pasted that JAR file over to my machine at home also using JDK 1.6.0 and NetBeans 5.5 on WinXP

I put the exact directory name where the JAR file resides, "C:\Program Files\Java\jdk1.6.0\classes", in CLASSPATH and rebooted my machine.

However, upon CD'ing to that directory and doing "java -classpath . GUI.jar", I get a "NoClassDefFoundError" when trying to do so.

Furthermore, I was not sure how to use NetBeans to run the JAR file to execute the classes within.

What did I do wrong? I'm so sorry this is so basic.

Thanx
Phil